JPH05136530A - Semicoductor laser device - Google Patents

Abstract

PURPOSE: To dispense with assembling individual parts later in a semiconductor device, by a method, wherein a quantum-well active region which is pinched between a pair of dispersion type plug reflection stacks is provided, a laser beam is emitted from the quantum-well active layer to the direction crossing a growth surface, an intrinsic semiconductor layer and a doped semiconductor layer are arranged on one side of the reflector stack, and an optical diode is formed. CONSTITUTION: A quantum-well active region 10 is arranged between a pair of dispersion type plug reflection stacks 11 and 12. An intrinsic semiconductor layer 13 and a doped semiconductor layer 14 are arranged on the dispersion-type plug reflection stack 11, and they form an optical diode on the path of a radiating light, together with an external layer. The intrinsic semiconductor layer 13 may be replaced with a plurality of quantum-well structures, in which a barrier layer and a quantum-well layer are arranged alternately. When the optical diode is biased, using annular ohmic contacts 16 and 17, either a laser output is monitored or a laser beam is modulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a self-monitorable vertical cavity surface emitting laser device suitable for forming a large planar array.

[0002]

Semiconductor laser devices are useful in many applications, such as optical interconnection of integrated circuits, communications, computer systems, and optical recording systems. A semiconductor laser device is a coherent, monochromatic, compact light source, which is modulated at a high bit rate to transmit much information. Since aging and temperature changes the output level of the laser, the semiconductor laser device generally requires a monitoring circuit because of the dynamic stability of its laser output.

Unfortunately, conventional edge emitting lasers are difficult to incorporate with other elements used in semiconductor laser systems. An edge-emitting laser emits coherent light along the surface of a buried plane parallel to the surface of its substrate. The direction of this laser emission is parallel to the growth surface in the semiconductor process. Therefore, edge emitting lasers are manufactured and tested as a single device. When using this edge emitting laser, a monitoring device and a photodiode which are manufactured separately are used in combination. Thus,
The manufacture of semiconductor laser systems generally requires time-consuming assembly work and alignment of multiple discrete components.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface emitting laser device capable of self-monitoring, which is simple and does not require subsequent assembly of individual components such as conventional edge emitting laser devices. To provide such a device.

[0005]

SUMMARY OF THE INVENTION A surface emitting semiconductor laser device of the present invention includes an integrated photodiode and / or a monitoring device and has a quantum well active region sandwiched between a pair of distributed Bragg reflector stacks. Then, laser light is emitted from here in a direction crossing the growth surface. The intrinsic semiconductor layer and the doped semiconductor layer are disposed on one of the reflective stacks and in combination with the outer layers of the stack form a photodiode in the path of the emitted light. This photodiode is used to monitor the laser power or to modulate the laser output. The semiconductor laser device of the present invention is particularly suitable for being formed and tested as a large array, and has the advantages of toroidal dispersion of light output, essentially single mode operation, and high two-dimensional packing density.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a quantum well active region 10 is located between a pair of distributed Bragg reflector stacks 11 and 12. An intrinsic semiconductor layer 13 and a doped semiconductor layer 14 are disposed on the distributed Bragg reflector stack 11.
These together with the outer layers of the stack form the photodiode in the path of the emitted light. Alternatively, the intrinsic semiconductor layer 13 may be replaced with a plurality of quantum well structures in which barrier layers and quantum well layers are alternately arranged. Photodiodes are used to monitor laser power and to modulate the laser beam.

The device of the present invention of this embodiment is formed on a substrate 15 doped with impurities of a first conductivity type (eg, n type). The quantum well active region 10 alternately has aluminum-gallium-arsenic barrier layers and gallium-arsenic quantum well layers. The distributed Bragg reflector stacks 11 and 12 periodically include a layer of doped aluminum gallium-arsenic and a layer of aluminum arsenic. In the distributed Bragg reflector stack 12 adjacent to the substrate 15, the aluminum gallium-arsenic is doped with the same type of impurities as the substrate (eg, n-type). In the distributed Bragg reflector stack 11 above,
Armygarium-arsenic is another type of impurity (eg p
Type) is doped.

The intrinsic semiconductor layer 13 is preferably intrinsic gallium-arsenic and the doped semiconductor layer 14 is preferably n-type aluminum gallium-arsenic. Annular ohmic contacts 16 and 17 are formed on the doped semiconductor layer 14 and the outer layer of the distributed Bragg reflector stack 11, respectively. The annular ohmic contacts 16 and 17, together with the ohmic contact 18 to the substrate, can provide suitable electrical biasing of either diode, or both diodes. When this laser diode is forward biased using an annular ohmic contact 17 and an ohmic contact 18, the active region 19 passes through the distributed Bragg reflector stack 11 and the intrinsic semiconductor layer 13 and the doped semiconductor layer 14. Emits light 20. In this structure, the intrinsic semiconductor layer 1
3 and the doped semiconductor layer 14 together with the outer layers of the distributed Bragg reflector stack 11 act as a photodiode formed in the path of the emitted light. The photodiode, when biased with annular ohmic contacts 16 and 17, is used to either monitor the laser power or modulate the laser beam.

FIG. 2 is an equivalent circuit of the photo diode / laser diode of FIG. The photodiode is shown as PD and the laser diode is shown as LD. With respect to ground, the laser diode voltage VPD and current are shown as IP. The laser diode voltage is VLD and the laser current is IL. P-DBR and N-DBR represent resistors represented as distributed Bragg reflectors.

When the photodiode current IP is applied to the fadeback circuit to control the laser current IL, this integrated circuit operates as a self-monitoring laser. On the other hand, when a modulation bias voltage is applied between VPD and ground, the change in bias changes the absorption coefficient and refractive index of the photodiode. This modulates the amplification and / or the phase of the laser output. In this mode, the device of the present invention operates as an integrated circuit laser and modulator.

The device of this embodiment is manufactured by molecular beam epitaxy (MBE). First, the first step provides an n-doped gallium-arsenide substrate 15 and MBE grows subsequent layers with the device of FIG. The apparatus of FIG. 1 includes a distributed Bragg reflector stack 1
2, a quantum well active region 10, a distributed Bragg reflector stack 11, an intrinsic semiconductor layer 13 and a doped semiconductor layer 14.

The distributed Bragg reflector stack 12 comprises three layers.
It is formed by growing a stepwise distributed Bragg reflector having zero period. Each cycle consists of 385 Å thick Al0.15Ga0.85As, 125 Å thick Al0.4Ga0.6As, 125 Å thick Al0.7Ga0.3As, 450 Å thick AlAs, and 125 Å thick. Strom thickness Al0.7Ga
0.3As and 125 Å thick Al0.4Ga0.6
It consists of As. This AlGaAs layer is doped with an n-type impurity, for example, silicon at a concentration of 10 ¹⁸ cm ^-3 .

Quantum well active region 10 is MBE and is grown on distributed Bragg reflector stack 12. As a preliminary step, a graded AlxGa1-xAs spacer layer is grown on the distributed Bragg reflector stack 12. The thickness of this spacer layer is preferably chosen such that the central antinode of the standing wave overlaps the quantum well. In this example, the thickness is about 2200 angstroms and x ranges from 0.6 to 0.3. The quantum well region grown on the spacer layer has four quantum wells,
These consist of a 100 Å thick GaAs well layer and a 80 Å Al0.2Ga0.8As barrier layer. Second 2200 Å thick graded Alx
A Ga1-xAs spacer layer grows on the quantum well layer. The two inclined spacer layers sandwich the quantum well active region to form a confinement hetero structure, and efficient carrier trap can be performed.

A distributed Bragg reflector stack 11 is grown on the quantum well active region 10, and in particular the quantum well active region 10.
On top of the upper graded spacer layer. The distributed Bragg reflector stacks 11 and 12 are almost identical, except that
The distributed Bragg reflector stack 11 is p-type doped rather than n-type, and the distributed Bragg reflector stack 11 has a smaller repetition period than the stack 12 and therefore emits light 20. In particular, the distributed Bragg reflector stack 11 is doped with Be at 3 × 10 ¹⁸ cm ⁻³ and has a repetition period of 20.

The intrinsic semiconductor layer 13 is formed by growing a layer of undoped gallium-arsenic on the p-doped outer layer of the distributed Bragg reflector stack 11. The thickness of the intrinsic semiconductor layer 13 is preferably half the wavelength of the emitted light, and the antinode is centered in the intrinsic semiconductor layer 13 for the purpose of efficient absorption. Doped semiconductor layer 1
4 is an n-type doped Al on the intrinsic semiconductor layer 13.
It grows as GaAs. The thickness of the doped semiconductor layer 14 is three quarter wavelengths, for example 1820 angstroms.

After the constituent layers have been grown, the next step is to form ohmic contacts and confine the current laterally. The annular ohmic contact 16 is a doped semiconductor layer 14
Each thickness is 120/270/50
0/1000 angstrom Au / Ge / Ag / Au
It is formed by depositing a mixed layer of. The mixed metal layer is lithographically patterned to have an outer diameter of about 2
An annular ohmic contact 16 having 0 micrometer and an inner diameter of about 10 micrometers is formed.

Photon injection (PRO) is preferably applied to the distributed Bragg reflector stack 11 after the formation of the annular ohmic contact 16.
TON IMPLANTION) to confine the current in the area under the ring. This photon injection protects the inner circle of the ring with a diameter of 15 micrometers, with a 6 micron thick photoresist concentric circle, and with a dose of 10 ¹⁵ cm ^-2 on this unprotected part. , 300 keV by exposure to photon injection. Photon injection at this energy produces an ionic dislocation profile that peaks at a depth of 2.5 micrometers. The device is then annealed at 450 ° C. for 30 seconds. As a result, the high resistance buried layer formed by the implant damage leaks current through the masked 15 micrometer diameter active region.

Using a 15 micrometer photoresist circle as an annular ohmic contact 16 and an etching mask, a 0.5 micrometer deep mesa was etched around the annular ohmic contact 16 to provide a distributed Bragg reflector stack. 11 on the AlGaAs surface.
Reactive ion etching is preferably used to obtain mesas with vertical side walls around the annular ohmic contact 16.

The annular ohmic contact 17 is formed with an exposed p-type doped Al0.15Ga0.85As layer, which is
Depositing a mixed layer of AuBe / Ti / Au each having a thickness of 800/200/1500 angstroms to form photolithographically an annular contact with an inner diameter of 30 micrometers and an outer diameter of 50 micrometers around the mesa. The same is done.

The final step is to form ohmic contacts 18 on the n-type doped gallium-arsenic substrate 15. This is similar to alloying the indium-doped substrate to copper heatsing (not shown). Thus, the device of the present invention is then tested. The characteristics of the device of the present invention are illustrated in Figures 3-5. Curve 1 in FIG. 3 shows the dark IV characteristics of the photodiode between the annular ohmic contacts 16 and 17, and curve 2 shows the annular ohmic contact 1.
7. Laser diode darkness IV between ohmic contacts 18
Show the characteristics. The forward characteristic of these two diodes is ideally twice the characteristic of the double heterostructure light emitting diode.

FIG. 4 shows the characteristics of the light output vs. current of the surface emitting laser. The solid curve represents the optical output power measured by an externally calibrated wide area silicon detector. The dotted curve represents the corrected photocurrent of the integrated photodetector / laser when the current due to spontaneous emission and the reverse leakage are subtracted. When the laser is forward biased between the annular ohmic contacts 17 and 18, at 3.2 mA threshold current, the device of the invention at room temperature exhibits a single axial mode and lateral direction. In mode, it lases with a continuous wave of 850 nanometers.

FIG. 5 represents the photodiode current at different reverse bias voltages as the forward injection current into the laser increases. In each case, the photodiode current increases rapidly at the onset of laser action. The output of the surface emitting laser is 0.24 mW, and with an efficiency response of 0.25 A / W, the corrected peak photocurrent (FIG. 3) is 60 microamps. Thus, for an output laser power of 100 microwatts, the integrated photodiode produces a photocurrent of 25 microamps, which is sufficient to stabilize the laser output.

The photodiode and modulator can be incorporated into a laser. For example, an integrated structure can be formed with the laser, the monitoring, the photodiode and the modulator on the opposite side. Further, while the gallium arsenide material system is preferred, other material systems such as indium arsenic are also used.

[0024]

The semiconductor laser device of the present invention is particularly well suited to be formed and tested as a large array, having an annular dispersion of light output, essentially single mode operation, and high two-dimensional packing density. There is an advantage.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

2 is a circuit diagram representing the interconnection between the diode and the laser of the device of FIG.

3 is a diagram showing a dark current-voltage characteristic of a diode of the device of FIG.

FIG. 4 is a diagram showing a light output-current characteristic of a laser diode of the apparatus of FIG.

FIG. 5 is a diagram showing a relationship between a photodiode current and a laser forward injection current at different reverse bias voltages.

[Explanation of symbols]

 10 Quantum Well Active Region 11 Dispersive Bragg Reflecting Stack 12 Dispersive Bragg Reflecting Stack 13 Intrinsic Semiconductor Layer 14 Doped Semiconductor Layer 15 Substrate 16 Annular Ohmic Contact 17 Annular Ohmic Contact 18 Ohmic Contact 19 Active Region 20 Optical

Continuation of the front page (72) Inventor Kouchi-te-U.S.A. 07060 Newge-Nose Plainfield, Willo-Avuenyu-38

Claims (7)

[Claims] 1. A surface emitting laser means having a quantum well region (10) arranged between a pair of reflective stacks (11, 12), and arranged in an optical path from an active region of the quantum well, Photodiode means (13,14) formed adjacent to one of the reflective stacks, said surface emitting laser means, and contact means (16,17,18) forming ohmic contact with said photodiode means. A semiconductor laser device comprising: 2. One of said pair of reflective stacks (12).
Has an n-type impurity-doped layer, the other (12) has a p-type impurity-doped layer, the photodiode means being one doped layer of the reflective stack. An intrinsic semiconductor layer disposed on the layer (13)
And the semiconductor layer (14) doped on the intrinsic semiconductor layer with an impurity of a different type than the doped layer. 3. The photodiode means comprises an intrinsic semiconductor layer disposed on the p-type layer of the reflective stack and an n-type semiconductor layer on the intrinsic semiconductor layer. The apparatus of item 2. 4. The device of claim 1, wherein the quantum well region comprises an aluminum-gallium-arsenic barrier layer and a gallium-arsenic quantum well layer. 5. The apparatus of claim 4, wherein the reflective stack comprises periodically layers of aluminum gallium-arsenic and layers of aluminum arsenic. 6. The device of claim 4, wherein the intrinsic semiconductor layer comprises gallium-arsenic. 7. An n-type gallium arsenide substrate, a first reflective stack grown on the substrate, wherein the reflective stack periodically includes an aluminum gallium-arsenic layer and an aluminum arsenic layer. A quantum well region grown on one reflection stack and the quantum well region include an aluminum-gallium-arsenic barrier layer and a gallium-arsenic quantum well layer, and the second reflection stack grown on the quantum well region and the second reflection stack. The reflective stack periodically includes a layer of aluminum gallium-arsenic and a layer of aluminum arsenic, and an intrinsic semiconductor layer of gallium arsenide grown on the second reflective stack and n grown on the intrinsic semiconductor layer. 2. The device of claim 1 having a layer of aluminum gallium arsenide of the type.